The present invention relates to the general field of turbine engine nozzles. It relates more precisely to the geometrical profile of nozzles of the convergent-divergent type.
Applications of the invention lie with bypass turbojets and turboprops for aircraft.
In known manner, a nozzle of a bypass turbojet comprises a central body, a primary cap arranged coaxially around the central body so as to co-operate therewith to define a primary flow channel for a hot stream, and a secondary cap arranged coaxially around the primary cap so as to co-operate therewith to define a secondary flow channel for a cool stream. When such a nozzle is of the convergent-divergent type, it presents a cross-section of the primary channel and/of the secondary channel that decreases going downstream prior to enlarging at its downstream end.
Likewise, a nozzle of a turboprop comprises a central body and an annular cap arranged coaxially around the central body so as to co-operate therewith to define an annular flow channel for a hot stream from the turboprop. When such a nozzle is of the convergent-divergent type, its channel presents a cross-section that decreases going downstream prior to enlarging at its downstream end.
Convergent-divergent nozzles of this type serve to improve the operability of the compressors feeding the nozzles (e.g. the fan in a nozzle of a bypass turbojet). Specifically, for a given throat section, a convergent-divergent nozzle makes it possible to obtain a flow rate on takeoff that is greater than is possible with a purely convergent nozzle.
Nevertheless, designing a nozzle of convergent-divergent type is an operation that is difficult and complicated; a poor design for the geometrical shape of a nozzle can greatly degrade its aerodynamic performance without achieving any improvement in the operability of the engine (i.e. in the controlability of the flow rate through the nozzle between two operating points of the turbine engine).